The objectives of this study focused on developing optimum alkaline-surfactant polymer (ASP) formulations for Nimr oilfield and to investigate the effect of nonionic surfactant iС13-O-(CH2CH2O)x-H (x = 10, 13, 18) molecular structure on the efficiency of ASP. Softened brine was used in this study. The cloud points of these surfactants at 0.1 wt% and 0.3 wt% were found to be higher than Nimr reservoir temperature (50 °C) in Na2CO3 concentration range 0.0-2.0 wt%, suggesting that all surfactants are compatible with softened brine in the presence of alkaline. Clear and stable solutions of surfactant (0.3 wt%) were also compatible with softened brine in the presence of the selected anionic polymer Flopaam-3630S (500 5000 ppm). Phase behavior of alkaline/surfactant (polymer)/brine/oil for all surfactants was used as a primary screening method to identify optimum emulsions at different water-to oil ratios (WOR = 90/10, 70/30 and 50/50). Activity maps were generated and showed the existence of optimum ASP formulations in a wide range of Na2CO3 concentration. The viscosity of Flopaam-3630S polymer at single shear rate of 2 s and different shear rates up to 100 ş" was investigated and showed good compatibility with the surfactant solution. At single shear rate of 2 s the experiment shows that 2000 ppm polymer without Na2CO3 and 2500 ppm polymer with 2.0 wt% Na2CO3 gave viscosity of around 100 CP which is the target viscosity of the ASP formulation and it was relatively stable up to shear rate of 100 s. There was no effect of surfactant addition to the viscosity of ASP sług. The promising formulations were validated by interfacial tension (IFT) measurements between the surfactant solution and crude oil. Dynamic IFT behavior was observed with all surfactants in which the IFT decreases rapidly to a transient ultralow minimum (DIFT min) then increases to an equilibrium value (IFT). Ultralow IFTs were generated with the surfactant and alkaline formulation. The lowest DIFTmin (5.4 x 103 mN/m) was obtained with iС13-O-(CH2CH2O10-H surfactant. This DIFTmin increased with an increase in the degree of ethoxylation. The addition of the anionic polymer resulted in an increase of the DIFTmir Finally, the optimum system Na2CO3 (2.0 wt%)/iС13-O-N(CH2CH2O)10-H (0.3 wt%)/Flopaam-3630S (2500 ppm) was selected for Nimr Oil and considered for further core flood tests.